Degradation of cellulosic insulation in power transformers. Part 2: Formation of furan products in insulating oil

The analysis of furan degradation products in transformer oil provides a co mplementary technique to dissolved gas analysis for monitoring transformer condition. The main products of the ageing are 2-furfuryl alcohol, 2-furald ehyde (furfural), 2-acetylfuran and 5-methylfurfural and are formed from wo od-based paper (containing lignin and hemicelluloses), cotton-based paper a nd pure cotton linters in accelerated, laboratory experiments. Also. 5-hydr oxy-methyl-cellulose was seen in the early stages of some experiments. The concentration of 2-furaldehyde (furfural) was round to be highest of all th e products and the concentrations of all products increased exponentially w ith time to a maximum value and then decreased. The concentration of most p roducts increased rapidly as the paper approached the end of its useful lif e, indicating that furfural analysis could provide a sensitive trouble-shoo ting tool for rapid ageing. All the furan products apart from 2-furfuryl al cohol are relatively stable in the oil, at temperatures up to 140 degrees C .